Cavity-type IC packages are useful in imaging devices such as CMOS imaging or CCD display applications for still or video cameras. The package includes a die at the base of a cavity and a clear lid epoxied on top. The use of a cavity-type IC package is advantageous for high frequency applications as the gold interconnect wires between the die attach pad and the contacts span an air gap rather than travelling through mold compound. The air has a lower dielectric constant than the mold compound and therefore the electrical impedance of the gold wire is much lower when the wire runs through air rather than through the mold compound. Thus signal distortion at high frequencies is inhibited.
Prior art cavity-type IC packages include ceramic body IC packages such as the Ceramic PGA cavity package traditionally used for microprocessors. However, these packages are cost prohibitive.
Other prior art packages include ball grid array (BGA) packages for use in imaging or camera applications. These packages are fabricated with a rim of high viscosity epoxy and a glass lid placed thereon. Again, these packages are cost prohibitive as they employ a substrate rather than a less-expensive leadframe.
The PANDA PACK, a well-known QFP (Quad Flat Pack) cavity style package, provides an air gap spanned by the gold interconnect wires. However, the inner leads of these packages are not supported and the mold flash must be cleaned from the leads for the gold wire to stick to the inner leads during wire bonding. Cleaning and wire bonding is difficult and therefore is not always successful.
Further improvements are driven by industry demands for increased electrical performance and decreased size and cost of manufacture.